Characterization of recombinant E. coli expressing arsR from Rhodopseudomonas palustris CGA009 that displays highly selective arsenic adsorption.

ABSTRACT

Innovative methods to lower arsenic (As) exposure are sought. The As regulatory protein (ArsR) is reported of having high affinity and specificity to arsenite [As(III)]. Rhodopseudomonas palustris CGA009 is a good model organism for studying As detoxification due to at least three ars operons and four diverse arsRRP1-4 on the genome. In this study, four Escherichia coli harboring arsRRP1-4 derived from CGA009 were engineered and tested regarding their As resistance. The results showed that E. coli (arsRRP2) displayed robust As(III) resistance, and its growth inhibition rate was only 2.9% when exposed to 3.0 mmol/L As(III). At pH 7.0, E. coli (arsRRP2) showed an enhanced As adsorption capacity. As(III) (2.32 mg/g (dry weight, dw)) and 1.47 mg/g arsenate [As(V)] was adsorbed representing a 4.2-fold and 1.3-fold increase respectively compared to the control strain. The adsorption process was well fitted to Langmuir isothermal mode. E. coli (arsRRP2) (1.0~12.0 g/L) could remove 30.3~82.2% of As (III) when exposed to 10 µg/L As(III). No increase in absorption to copper(II), zinc(II), chromium(III), and lead(II) could be detected. Our studies revealed that arsRRP1-4 from CGA009 could confer As(III) resistance; E. coli (arsRRP2) displayed the highest As resistance, selectivity, and adsorption capacity within a wider pH (5.0~9.0) and salinity (0~15.0 g/L NaCl) range, especially important as it could remove As(III) from low concentration As-containing water.